Did you consider alternate approaches like using Ansible to give you more native system options as well, or was the goal here truly to have something 100% cross platform on anything? A hybrid might be a good approach too. Personally I think I'd end up backsliding because if I'm using a platform I really like then I want to be able to take advantage of some of its best native software and interface bonuses, so a purely X-based setup will still lead me to some manual setup on my own systems. Once stuff out of the automatic flow crept in feels like it might build up over time since I'm not that disciplined. Some of the playbooks I've seen though could be enhanced further with this, neat project.

> if I'm using a platform I really like then I want to be able to take advantage of some of its best native software and interface bonuses

This is precisely why I built Darch (https://godarch.com). I wanted an immutable OS, but also to take full advantage of my hardware, completely native. Your images show in in grub and you can boot right into them.

I have explored that approach, using Ansible, and I think it is promising. I earlier tried an approach with Vagrant and Virtualbox but the non-nativeness of my environment were causing more problemn than it solved.